refactor(tests): convert attendance warning email test to delivery assertions

Replaces spy-based mock test with email delivery verification.

Changes:
- 'sends an attendance warning email' - finds email by recipient and subject
- Uses flexible matching to account for other emails in deliveries

Removes allow().to receive() and have_received() mocks

Author: mroderick

spec/models/attendance_warning_spec.rb

@@ -10,11 +10,10 @@
     end
 
     it 'sends an attendance warning email' do
-      allow(MemberMailer).to receive(:attendance_warning).with(member, member.email).and_call_original
-
       described_class.create(member: member, issued_by: admin)
 
-      expect(MemberMailer).to have_received(:attendance_warning).with(member, member.email)
+      email = ActionMailer::Base.deliveries.find { |e| e.to.include?(member.email) && e.subject.include?('Attendance') }
+      expect(email).not_to be_nil
     end
 
     describe '.scopes' do